Electric disconnect switch and method of making switches



May 19, 1970 I R. P. BRIDGES 3,513,272

ELECTRIC DISCONNECT SWITCH AND METHOD OF MAKING SWITCHES Filed Nov. 29, 1968 4 Sheets-Sheet 1 1;, HHHII I May 19, 1970 R. P. BRIDGES 3,513,272

ELECTRIC DISCONNECT SWITCH AND METHOD OF MAKING SWITCHES Filed Nov. 29. 1968 4 Sheets-Sheet 2 FIE. 3 55 Hi HUM u.

F1 E 4 /4 j J 115 50 J/ 45 a 390 40 4a R. P. BRIDGES May 19, 1910 ELE TRIC DISCONNECT SWITCH AND METHOD OF MAKING SWITCHES .4 SheetsSheet 3 Filed Nov. 29, 1968 May 19, 1970 R. P. BIRIDGES ELECTRIC DISCONNECT SWITCH AND METHOD OF MAKING SWITCHES Filed Nov. 29, 1968 4 Sheets-Sheet 4 45 44? United States Patent US. Cl. 200-48 Claims ABSTRACT OF THE DISCLOSURE An electric disconnect switch for high voltage and amperage service in which the switch body and blade are.

made of a metal such as aluminum which has high electrical conductivity with a surface that has low electrical conductivity, in which the switch body and blade are provided with contacts of a high electrical conductivity material such as silver that are joined to the body and blade through copper studs in such a way as to minimize galvanic corrosion, and to maintain a tight fit between the contacts and the switch body and blade in spite of the dilferent temperature coeificients of expansion of copper and aluminum; and a method of making such switches.

BACKGROUND OF THE INVENTION Electric disconnect switches for high voltage and amperage service must be made of a material which has a very high coefficient of electrical conductivity, and for many years copper alloys were the preferred material for such switches for this reason. However, in recent years it has become increasingly desirable to fabricate such disconnect switches from aluminum alloys. Aluminum is an excellent electrical conductor and is much more economical than copper alloys on an equal current-carrying basis. Furthermore, the relatively light weight of aluminum components permits lighter weight brackets and insulators, and the lighter weight units are easier to handle in installation and replacement.

Another reason for making disconnect switches from aluminum is that electrical substations contain more and more aluminum bus and the aluminum switch eliminates the need for bi-metallic connections between the bus and the switch and is compatible from an appearance standpoint.

Aluminum switches, however, present serious problems because the surface of an aluminum alloy is not a good conductor so the contact points between the switch and the blade must be of a metal other than aluminum. Silver or silver alloys are among the best materials available for contact purposes, but silver is incompatible with aluminum because of a highrate of galvanic corrosion between the two metals. Prior art attempts to provide silver contacts on aluminum switches have generally been expensive, clumsy and disadvantageous in various other respects.

Another serious problem with connecting silver contacts to aluminum switches is that the temperature coefiicients of expansion of the two metals are considerably different, so that the contacting surfaces of the two metals tend to move apart with temperature changes.

SUMMARY OF THE INVENTION In accordance with the present invention, a silver switch contact is mounted on an aluminum disconnect switch by brazing a thin coin silver contact to a copper stud. The stud and silver contact are then hot-tin-dipped, and the tinning is machined off of the silver surface to expose the bare silver. The stud has a shank which is the same diameter, before tinning, as a hole in the aluminum switch member to which it is to be connected, and the shank is ice longer than the thickness of the switch member and. has an enlarged head at one end.

The copper stud is cooled to approximately 0 F. and the aluminum switch member is heated to approximately 200 F. and the copper stud is then driven into the hole with which it has a heavy interference fit under those temperature conditions.

Subsequently the projecting end of the shank of the stud is forged under a pressure of approximately 8 tons, so that the cooper stud has a flange formed at the end opposite the enlarged head, and the switch member is firmly clamped between the head flange and the forged flange. Before the stud and the switch member are assembled the mating surfaces are coated with a commercially available lithium base grease-like material which is a good electric conductor but prevents any corrosive liquids or gases from entering the contact areas between the tin coated cooper stud and the aluminum.

The foregoing construction has two particular advantages. In the first place, differential expansion and contraction of the aluminum and the cooper due to their different temperature coefficients of expansion never results in any reduction in the firmness of the surface contact between the copper stud and the switch body or blade because of the contacting surfaces at right angles to each other. Thus, for example, if the assembly is initially at a low temperature in outdoor service and the temperature increases because of weather or electrical loads, a more rapid expansion of the aluminum than of the copper increases the pressure between the flanged surfaces of the copper member and the aluminum body or blade. Conversely, as the assembly cools the aluminum contracts at a faster rate than the copper and tends to increase the contact pressure on the shank of the stud.

In the second place, the normal galvanic or electrolytic corrosion which occurs relatively rapidly between silver and aluminum in the presence of corrosive liquids or gases is minimized by arranging the metals in contact in the proper sequence from the most noble to the least noble metal (silver-copper-tin-aluminum). Galvanic corrosion is also minimized by sealing the contact area as previously described, and by providing an extremely high ratio of exposed aluminum surface to exposed silver surface so as to minimize galvanic attack on the aluminum.

While the double-headed stud previously described is the most desirable type of contact assembly, in multiple contact assemblied it is necessary to have one adjustable contact so that all contact points carry their share of the electrical load. To provide for this in the present construction the contact on the switch body is by means of a threaded tin-plated copper stud which has the silver contact at one end and a jam nut at the other end to pull the threads of the stud into firm contact with the threads of the aluminum switch body.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary plan view of a switch structure embodying the invention, and illustrating the makeand-break contacts of a switch body and dual knife blade switch;

FIG. 2 is a fragmentary side elevational view of the structure of FIG. 1;

FIG. 3 is a sectional view taken substantially as illustrated along the line 33 of FIG. 1;

FIG. 4 is an end elevational view of the structure of FIG. 1 taken substantially as indicated along the line 4-4 of FIG. 1;

FIG. 5 is a fragmentary plan view of the pivot end of a switch the make'and-break end of which is illustrated in FIG. 1;

FIG. 6 is a fragmentary side elevational view of the structure illustrated in FIG. 5;

FIG. 7 is a fragmentary section on an enlarged scale taken substantially as illustrated along the line 77 of FIG. 1 and of FIG. 2;

FIG. 8 is a fragmentary section on an enlarged scale taken substantially as illustrated along the line 8-8 of FIG. 5 and FIG. 6.

FIG. 9 is a longitudinal central sectional view of the contact stud assembly seen in FIG. 7 before the stud is forged onto the switch blade member; and

FIG. is a longitudinal central sectional view of the contact stud assembly seen in FIG. 8 before the stud is forged onto a switch member.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings in greater detail, and referring first to FIGS. 1 and 5, a typical electric disconnect switch to which the structure of the present invention may be applied consists of switch body means including a switch pivot body member 10a and a switch contact body member 10b. The members 10a and 10b are commonly mounted on a support bar and insulators (not shown) as illustrated in Bridges Pat. 3,205,330. A switch blade member, indicated generally at 11, consists of a pair of parallel blades 11a and 11b which are connected at intervals by cross members 12 and pivotally mounted at 13 upon the switch pivot body 10a. At the free end of the switch blade 11 is a latch structure, indicated generally at 14, and contact means indicated generally at 15. The switch body members 10a and 10b and the switch blade means 11 are cast from an aluminum alloy commonly used for electrically conductive parts, the preferred alloy being one which is commercially available as a 6061-T6.

Referring now to FIGS. 5 and 8, the pivot means 13 includes a pair of hollow copper alloy studs, indicated generally at 16, which are mounted in aligned holes in opposite walls 100 of the switch body pivot member 10a; and another pair of hollow copper alloy studs 16 which are mounted in the switch blade members 11a and 11b.

The hollow copper studs 16 are preferably fabricated from tellurium copper rod, Grade ASTM B301. FIG. 10 illsutrates a hollow stud 16a before it is forged onto a switch body or blade members as illustrated in FIG. 8; and the stud is seen to include a shank 17 and a flange 18 with the hollow stud 16a having a bore 19 and a counter bore 20 connected by a chamfer 21. Preferably the hollow stud is provided with a silver contact ring 24 which is secured to the surface 18a of the copper stud by a braze 25. However, for some applications direct copper to copper contact is satisfactory between the hollow copper studs 16 on the body member and the blade member. The entire stud 16a is covered with a hot-dipped tin coating 22 the thickness of which is exaggerated in FIG. 10 to make it visible. In actual fabrication of the stud 16a the entire stud is hot-tin-dipped and the tin is then machined off of the silver ring 24, or off of the outer surface of the flange 18 if the silver contact is not used.

Each of the hollow studs 16 is mounted in the body member or the blade member, as the case may be, by the method heretofore described. That is, the hollow copper stud is cooled to a temperature of approximately 0 F. and the aluminum member is heated to approximately 200 F. the diameter of the shank 17 before tin-dipping and before cooling is exactly the same as that of the hole in the aluminum member into which the hollow stud fits; so with the tin coating on the stud it makes a snug sliding fit in the heated aluminum blade member. Thus, as the parts are permitted to return to ambient temperature the aluminum member makes a strong shrink fit upont he copper member. At this point an end portion 23a of the shank 17 is projecting a short distance from the aluminum member with which the hollow stud is assembled, and that projecting end portion 23a is forged under a pressure of approximately 8 tons, applied in a transverse direction, to produce a formed flange 23 on the hollow stud 16 and firmly grip the aluminum body or blade member between the flange 18 and the formed flange 23.

The pivot assembly is completed by inserting a tubular aluminum spacer 26 between the hollow studs 16 in the switch pivot body member 10a and inserting a stainless steel bolt 27 with stainless steel bellville washers 28 beneath the bolt head 27a and beneath a nut 29.

Referring now to FIGS. 1 to 4, the latch structure 14 which is mounted at the free end of the switch blade means 11 is generally conventional, and includes a bifurcated link member 30 which is supported between the blades 11a and 11b upon a cross pin 31 and a bolt 32. Pivotally mounted upon the cross pin 31 is a latch ring 33, while rotatably mounted upon the bolt 32 is a latch member 34 which is connected to the ring member 33 by means of a tension spring 35. The latch member 34 has an actuating finger 34a which is engaged with a projecting nose 33a upon the latch ring 33, and a latch hook 34b on the latch member 34 engages beneath a latch flange 36 which is cast integrally with the switch body contact member 10b. It is apparent from FIG. 3 and from the foregoing description that the blade 11 may be unlatched from the switch body contact member 10b by pulling up on hook stick ring 33b of the latch ring 33 so as to pivot the ring around the pin 31 and thus rotate the latch member 34 clockwise by engagement of the latch ring nose 33a with the latch member actuating finger 34a. This swings the latch hook 34b out from beneath the latch flange 36 and releases the blade 11 for pivotal movement about the pivot means 13.

The switch contact means 15 comprises three blade contact assemblies 37 on each of the blade members 11a and 11b, and three matching switch body contact assemblies 38 on each side of the switch body contact member 10b which are in position to make contact with the blade contact members 37 when the switch blade is in the closed position illustrated in the drawings. Bearing on the blade contact elements 37 through guide plugs 39 are compression springs 39a which are clamped under trefoil pressure plates 40 the central portions of which are clamped under nuts 32a that screw onto threaded end portions of the bolt 32. Referring now particularly to FIGS. 7 and 9, each of the blade contact members 37 comprises a tellurium copper stud, indicated generally at 41, which has a shank 42 and a head flange 43. The shank is bored out at the end opposite the head flange 43 to provide a cylindrical wall 44. A silver contact disc 45 is secured to the head flange 43 by means of a braze 46, and the entire contact except for the silver disc 45 is coated with tin by hot dipping. As in the case of the hollow pivot studs previously described, the entire stud including the silver contact disc 45 is hot-tin-dipped, and the tin coating is then machined off the silver disc.

Assembly of each of the contact studs 41 with a blade member 11a or 11b is the same as that heretofore described for the hollow pivot studs. After the studs 41 are assembled with the blade members by a shrink fit a part of each of the annular stud walls 44 is projecting from the outer surface of the switch blade member, and this projecting end portion is forged under a transverse pressure of approximately 8 tons to form flanges 48 so that the blade members are firmly gripped between the head flanges 43 and the formed flanges 48.

Referring further to FIG. 7, the switch body contact members 38 consist of threaded tellurium copper studs 49 which have bores 50 at one end to receive silver contact rivets 51. Each threaded stud 49 is provided with a kerf 52 by means of which it may be screwed into a threaded hole in the body member 10b, and after each of the threaded studs 49 is positioned to have the desired amount of bearing force upon the mating blade contact 37 a jam nut 53 is screwed onto the projecting threaded end of the stud 49 so as to lock the latter firmly in place and force the threads 49:: of the stud firmly into engagement with the matching threads (not shown) in the switch body. As in the case of the contact studs previously described, the threaded studs 49 are hottin-dipped and the hot tin is then ground off of the head of the silver contact rivet.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. In an electric disconnect switch which has a body member and a blade member of a first metal and electric contact means on the body member and the blade member, said contact means being of a second metal which has a different temperature coefficient of expansion than the first metal, the improvement which comprises: contact means comprising a stud which has a shank that fits tightly in a hole in a switch member to provide a first pair of contacting surfaces, and radial flanges at the two ends of said shank with said switch member clamped firmly therebetween to provide a second pair of contacting surfaces at right angles to said first pair, Whereby differential expansion of the means and the member because of an increase in temperature tightens the contact between one of said pairs of contacting surfaces while differential contraction between the means and the member because of a decrease in temperature tightens the contact between the other of said pairs of contacting surfaces.

2. The switch of claim 1 in which the stud is unitary.

3. The switch of claim 1 in which the contact means on the blade member comprises a one-piece stud, in which the body member has a threaded hole aligned with said stud, there is a contact means comprising a stud with a threaded shank screwed into said hole with an end portion remote from the blade member projecting transversely from the body member, and in which a threaded jam nut is screwed onto said projecting end portion.

4. The switch of claim 1 in which the switch body and blade are aluminum and the stud is copper.

5. The switch of claim 4 in which a silver disc is mounted on one end of the stud, a braze connects said disc to said stud, and a coating of tin covers the stud.

6. In an electric disconnect switch which has a body member, and a blade member pivotally connected to the body member, both of said members consisting of a metal which has a high coeflicient of electrical conductivity with a surface that has a relatively low coefficient of electrical conductivity, contact means providing a path of high electrical conductivity through the switch body and blade members comprising: first contact means associated with the pivoted connection between the members, said first contact means including a pair of aligned hollow studs of high electrical conductivity, one of said studs being fitted tightly in a hole in the body and the other of said studs being fitted tightly in a hole in the blade, said studs having abutting contact surfaces; a pivot pin which connects the blade and the body extending through said hollow studs; and resilient means urging said abutting contact surfaces into contact with one another.

7. The switch of claim 6 in which the abutting contact surfaces comprise a pair of silver rings, and a braze secures each silver ring to a stud.

8. The switch of claim 6 which also includes contact means on the body member and the blade member at a position remote from the pivotal connection between said members, said contact means including a first stud of high electrical conductivity which has a shank that is tightly fitted in a hole in the blade and radial flanges at the two ends of the shank with the blade member clamped firmly therebetween, one of said flanges facing the switch body member; a first silver disc, a braze sel the flange abutting the member and the end of the stud curing said first disc to said one of said flanges, a second stud of high electrical conductivity having a threaded shank screwed into a threaded hole in the switch body in alignment with the first stud, said second stud having a first end projecting from a face of the body adjacent said one flange of the first stud and having a second end projecting from an opposite face of the body, a second silver disc abutting said first silver disc, a braze connecting said second disc to said first end of said second stud, and a jam nut on the second end of the second stud.

9. The switch of claim 6 in which the body member and the blade member are aluminum, the hollow studs are copper and said studs are coated with tin.

10. The switch of claim 7 in which the body member and the blade member are aluminum, the hollow studs and the first and second studs are copper, and all said studs are coated with tin.

11. In an electric disconnect switch which has pivotally connected aluminum body and blade members with silver electric contact surfaces on said members, the improvement which comprises: a tin coated copper stud firmly mounted in each member to provide a support, said studs having juxtaposed ends; a pair of face abutting silver elements on said juxtaposed ends; and a braze connecting each of said elements to a stud.

12. The switch of claim 10 in which the studs are mounted in the switch body and blade members in locations remote from the pivotal connections between said members, the studs have shanks which are solid, and the silver elements are discs.

13. The switch of claim 11 which includes hollow studs, silver elements in the form of rings on said hollow studs, and a pin extending through said studs and rings to provide the pivotal connection between the body and blade members.

14. The switch of claim 10 in which the studs are hollow and the silver elements are in the form of rings on said hollow studs, and in which a pin extends through said studs and rings to provide the pivotal connection between the body and blade members.

15. A method of mounting silver contact elements in a hole that extends through an aluminum switch member, said method comprising the steps of: providing a copper stud which has a shank the diameter of which is substantially equal to the diameter of the hole and the length of which is substantially greater than the thickness of the switch member, said stud having a flange at one end; brazing a silver disc to said flange; hot tin dipping the stud; machining the tin off the silver disc; cooling the stud and heating the switch member; inserting the cooled stud into the hole of the heated switch member with opposite the flange projecting from the member; permitting the stud and switch member to return to ambient temperature to shrink the member onto the stud; and forging the projecting end of the stud against the member under heavy pressure to form a flange and thereby clamp the member between the flange and the formed flange.

References Cited UNITED STATES PATENTS 2,786,923 3/1957 Kleb. 2,836,688 5/1958 Florschutz. 2,895,033 7/1959 Favre.

ROBERT K. SCHAEFER, Primary Examiner H. J. HOHAUSER, Assistant Examiner US. Cl. X.R. 200-166, 

